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<br />Many high altitude, ground-based seeding experiments were conducted during the multi-winter <br />research program on the Wasatch Plateau of central Utah summarized by Super (1999b). Either <br />AgI or liquid propane was released well up the windward slope about 1000 ft vertical distance <br />below the plateau top. Sometimes a tracer gas was simultaneously released to permit detailed <br />plume definition using a fast-response detector. Results from these experiments have been reported <br />by Super and Holroyd (1994), Super (1995), Super and Holroyd (1997) and Holroyd and Super <br />(1998) and Super and Heimbach (2005b). Holroyd et al. (1995) discussed an additional experiment <br />where both AgI and tracer gas were released from another high altitude site 1850 ft below the <br />plateau top. <br /> <br />There is no point in belaboring this issue. Quite simply, every published observational study the <br />authors are aware of which tracked plumes from high elevations releases, more than 1/2 to 2/3 of <br />the way up windward slopes, demonstrated routine plume transport over the mountain barrier. Of <br />course, the wind in the layer between the high elevation seeding site and the ridgeline must have a <br />significant cross-barrier component for such transport to occur. When that is the case, high <br />elevation releases will result in the seeding agent reaching SL W cloud to a height of about 2000 ft <br />above the crestline. Whether the SL W cloud is cold enough for effective AgI seeding and whether <br />growth and fallout times are adequate for meaningful snowfall are separate issues. <br /> <br />7. Propane Seeding Potential in Colorado <br /> <br />This section is brief because thorough discussions of propane seeding in general, and the <br />results of the Utah randomized seeding experiment, are contained in the peer-reviewed article by <br />Super and Heimbach (2005a), and in more detail in the final report by Super and Heimbach <br />(2005b). The development of radio-controlled propane dispensers for use on California's Sierra <br />Nevada has been discussed by Reynolds (1996) and a number of his articles cited therein <br />including Reynolds (1989). Since all this information is readily available, it will not be repeated <br />here except that the summarized conclusions of Super and Heimbach (2005a) on the Utah winter <br />of 2003/2004 randomized experiment have been extracted and are paraphrased below. There. <br />were a total of98 experimental units (EUs) produced by this experiment. Each EU had a 40 min <br />release of propane which was separated from adjacent releases by 20 min buffers. The Utah <br />results are expected to be transferable to Colorado because of similarities in SL W cloud <br />characteristics presented in this report. <br /> <br />. Tests of the entire sample of98 EUs without any partitioning were strongly suggestive of <br />a real seeding effect of increased snowfall at a target gauge on the windward slope and <br />the two target gauges on the west edge of the Wasatch Plateau. <br /> <br />· Results for the 98 EUs were inconclusive at the most downwind gauge just 1.2 miles east <br />of the plateau top's west edge, meaning no valid conclusion can be made whether seeding <br />was effective there or not. Frequent mistargeting of that gauge was possible. <br /> <br />· Results for the 69 EUs partitioned by southwest quadrant seeding site winds, known to <br />transport seeding plumes from the high altitude release point over the primary target, <br />were also strongly suggestive of snowfall increases at the target gauges on west edge of <br />the plateau top. Results were somewhat suggestive at the windward gauge closest to the <br />propane dispensers, and also at the downwind gauge furthest from the seeding location. <br /> <br />23 <br />